Analysis and Design of Integrated Magnetorquer Coils for Attitude Control of Nanosatellites Hassan Ali*, M. Rizwan Mughal*†, Jaan Praks †, Leonardo M. Reyneri+, Qamar ul Islam* * †Department of Electrical Engineering, Institute of Space Technology, Islamabad, Pakistan, †Department of Electronic and Nano Engineering, Aalto University, Espoo, Finland +Department of Electronics and Telecommunications, Politecnico di Torino, Torino, Italy Abstract—The nanosatellites typically use either magnetic rods or become a challenge. In order to stabilize the tumbling satellite, coil to generate magnetic moment which consequently interacts the attitude control system is very necessary. There are two with the earth magnetic field to generate torque. In this research, types of attitude control systems i.e. passive and active [1-6]. we present a novel design which integrates printed embedded The permanent magnetics and the gravity gradients are passive coils, compact coils and magnetic rods in a single package which type. They being cost effective, consume no power but no is also complaint with 1U CubeSat. These options provide maximum flexibility, redundancy and scalability in the design. pointing accuracy is achieved using these types of actuators. The printed coils consume no extra space because the copper The majority of the missions these days require better pointing traces are printed in the internal layers of the printed circuit accuracies. The active control systems are typically used for in board (PCB). Moreover, they can be made reconfigurable by missions where better pointing accuracy is desired. The printing them into certain layers of the PCB, allowing the user to magnetorquer is a good option to control the attitude of select any combination of series and parallel coils for optimized nanosatellite. They use the local (earth) magnetic field to design. The compact coil is wound around the available space in generate the torque, which is used to rotate the satellite. a 1U complaint CubeSat panel and it can accommodate much In this work, we present a combined design of attitude more number of turns compared to printed coil; consequently generating more torque. The magnetic rod is made complaint control system by combining different types of magnetorquers with the existing available options and can easily be integrated in to overcome the main constraints like available power, cost, the panel. This design gives a lot of flexibility because one can mass and space availability. The printed or embedded coil, choose to optimize power, optimized torque or rotation time by compact coil and cylindrical rod are combined in a CubeSat choosing among the available magnetorquer options. The complaint panel to achieve three axis control. The detailed proposed design approach occupies very low space, consume low analysis has also been performed for all the types and the power and is cost effective. proposed design is also compared with the commercial designs. The analysis in terms of generated torque with certain applied The thermal analysis has also been presented for the proposed voltages, trace widths. The analysis results in terms of selection of design. optimized parameters including torque to power ratio will be presented. The ACS manages the satellite orientation, in order to point its antennas toward ground station or solar panels towards the sun. For this purpose normally permanent magnets, Keywords—ADCS; Magnetorquer; Reconfigurable; Printed; Compact; Optimum; magnetorquer Rod; Nanosatellite; reaction wheels and magnetic rods are used. Permanent magnets are cheap, simple, light and consuming no power. But they have inadequate pointing accuracy and give very little choices on the pointing direction. Reaction wheels and I. INTRODUCTION magnetic rods have better pointing accuracy and can orientate With the passage of time, the size of the satellites is satellite in any direction but their price, weight and size make reducing and their applications are increasing. Due to their low price, mass and size, it has become more attractive for them incompatible with CubeSats standard Nanosatellites like universities, small research organizations and space agencies to AraMiS-C1. build, test and launch their own satellites. With the reduction of The best solution to this problem is the design of size of the CubeSats and nanosatellites, the designing and reconfigurable magnetorquers which are able to produce placement of all the subsystem in a reduced space has also required magnetic moment and consequent torque for any desired spacecraft configuration. The design having printed magnetorquers, compact magnetorquers and magnetic rods has been accomplished for iCube and AraMiS satellites [8-9]. The design approach is based on smart panels which can be integrated together to form any CubeSat configuration [8-9]. A panel showing printed magnetorquer in the internal layers is shown in Fig.1. Fig.2 Flow diagram of the system A completed flow diagram of the system is shown in Fig. 2. The attitude of the spacecraft is determined with the help of certain attitude sensors and this attitude information is sent to on board data handling system (OBDH) with the current and target attitude. The OBDH sends torque commands to actuate either compact, printed or magnetic rod after calculations of desired torque for desired attitude attainment. The new attitude is fed back to the onboard computer and the loop repeats. This work suggests an optimized combined design where these attitude control solution are used by optimizing certain parameters like trace widths, applied voltages, to generate torques while keeping torque to power ratio optimized. The theoretical design has been verified by experimental setup. II. MGENETORQUER DESIGN A. Printed Magnetorquer Fig.1 Design of printed coil on a CubeSat panel The printed magnetorquer design is selected by performing the theoretical calculations on generated torque, torque to power The printed Magnetorquer is a better choice for attitude ratios for CubeSat complaint panels by changing the applied control and stabilization of Nanosatellites when the mission voltage. The designed printed magnetorquer is fully compliant with the CubeSat dimension and requires no extra space since requires less torque and less power consumption. The compact the traces are embedded in the internal layers of the board. The magnetorquer is suitable for better pointing where consuming board has been designed using optimal parameters including more power to generate more torque. The cylindrical solution the selection of outer and inner copper dimensions, trace provides best pointing but it needs more area, power to widths, distance between two adjacent traces and power generated torque. consumption analysis vs the generated torque. The copper traces of magnetorquer coil are printed into the inner layer of The goal of this work is to provide CubeSats with printed circuit board (PCB). The selected dimensions of the reconfigurable option of using all the possible magnetorquers printed magnetorquer are shown in Fig.3. keeping power, torque, and torque to power optimized [7]. By increasing turn width, the torque increase but at the expense of temperature rise as evident from the Fig.4. Fig.3 Dimensions of printed coil After the analysis part, the optimum placement of printed coil on a 1U complainant panel is performed. Each coil trace has a width of 0.5 mm and thickness of 18 µm. Each turn is approximated like square, separated by 0.2 mm distance and has four sides. For our panel design which can be integrated into CubeSat dimensions, the single coil has a bundle of 42 turns in a single Printed Circuit Board layer and has a bundle width of 30 mm with outer dimensions being 90 푚푚 × 90 Fig. 4 Turn width Vs Torque, τ /P, Power and current for 푚푚 and inner dimensions being 30 푚푚 × 30 푚푚. printed magnetorquer The cross sectional trace area (width and thickness), length The relation between applied voltage and torque, torque to and number of turns of coil affect the resistance of the power ratio and temperature of the coil at specified turn width, magnetorquer coil which is related to the parameters like external and internal side length is shown in Fig.5. By torque, power and heat generated for target maneuver. The key increasing the applied voltage, the generated torque and parameters related to the design are discussed in the coming temperature is increasing due to large consumption of power at sections. The design parameters of embedded magnetorquer higher voltages. The torque to power ratio is decreasing as the coil are shown in table 1. applied voltage is increasing as shown in Fig.5 The analysis Table 1 suggests that better torque to the power ratio is achieved at lower working voltages. Embedded magnetorquer coil parameters of single layer Parameter Values Single turn average length 240 mm Length of single coil 10,080 mm Outer-most turn side 90mm Inner-most turn side 30mm Trace thickness 1.8 µm Trace Width 0.5 mm Area occupied by turns(1 layer) 0.1671 m^2 Distance between two adjacent traces 0.2 mm Copper resistivity 1.7*10^-8 Nominal Magnetic moment(by 1 layer) 0.0284 Am^2 Working voltage 2V to 7V The optimization of our design is based on applied voltage, generated torque and T/P Ratio. It is apparent from the graphs of Fig.4 that the torque to power ratio is decreasing by increasing the turn width therefore we conclude that; the smaller the turn width, the greater the torque to power ratio. Fig.5 Voltage Vs Torque, τ /P and temperature for printed magnetorquer B. Compact Magnetorquer The compact magnetorquer coil is wound on the surface of the panel printed circuit board for generation of better torque with the applied voltage. The laminated copper wire is wounded around the panel such that the coils are held on the top of the surface. The external most dimension of winding structure is 90mm × 90mm and the height of coil is 5mm for turns of specified gauge of wire.